class Parent {
    title:string = "默认值";
    show(){
        console.log(this.title);
    }
}


class Child extends Parent {
    info:string = "child"
    print(){
        console.log(this.info);
    }
}

var p:Parent = new Parent();
var c:Child = new Child();
var d:Parent = new Child();
var e:Object = new Child();